The angular resolution of telescopic arrays used in direct-detection interferometric measurement can be enhanced by increasing the baseline size, i.e., the distance between telescopes. The telescopes are used to observe the interference pattern of light coming from the source, with the latter providing information about the correlation function of the radiation from distant objects, such as stars and other astronomical objects, for example. Experimentally, the interference pattern is used to measure the amplitude and phase of the complex visibility function from which the source intensity distribution can then be calculated. Increasing the baseline of the telescope array for visibility measurements while maintaining sensitivity can improve the resolution of the source intensity distribution. However, one problem with the direct-detection interferometric method is the loss of photons during transmission between the telescopes in an array. Longer baselines lead to higher photon loss resulting in lower rates of successful interference events, which reduces the scheme sensitivity. Thus, an increase in resolution is generally accompanied by a loss in sensitivity of interferometric measurements using telescopic arrays.
A way to mitigate this problem using mode-entangled photons has been proposed in D. Gottesman, T. Jennewein, and S. Croke, “Longer-Baseline Telescopes Using Quantum Repeaters,” Phys. Rev. Lett. 109, 070503 (2012), herein incorporated by reference in its entirety. Their main idea was to distribute known and replaceable photons in a perfect Bell-state between two telescopes in advance, utilizing a quantum network, and extract the visibility function from local measurements, therefore eliminating the propagation loss of the collected photons. However, technologically it is infeasible to reliably distribute perfectly entangled quantum states over long distances. This is because the enabling technology of long-lifetime quantum memories, decoherence-free entanglement swapping mechanisms, high-fidelity quantum gates for purification, distillation and error-correcting protocols is not mature enough to yield distributed states with fidelities close to perfectly-entangled Bell-states.